docs: def sequence_type(self):
          '''Guess the type of input sequence provided to graftM (i.e. nucleotide
          or amino acid) and return'''
          if self.known_sequence_type is not None:
              return self.known_sequence_type
          else:
              # If its Gzipped and fastq make a small sample of the sequence to be
              # read
              cmd='%s | head -n 2' % (self.command_line())
              first_seq = subprocess.check_output(
                                                  cmd,
                                                  shell=True,
                                                  preexec_fn=lambda:signal(SIGPIPE, SIG_DFL)
                                                  )
              _, seq = tuple(first_seq.strip().split('\n'))
              self.type = self._guess_sequence_type_from_string(seq)
              logging.debug("Detected sequence type as %s" % self.type)
              return self.type